Solid-phase extraction characteristics

Principles and Characteristics Solid-phase extraction (SPE) is a very popular sample preparation and clean-up technique. In SPE solutes are extracted from a liquid (or gaseous) phase into a solid phase. Substances that have been extracted by the solid particles can be removed by washing with an appropriate liquid eluent. Usually, the volume of solvent needed for complete elution of the analytes is much smaller (typically < 1 mL) than the original sample volume. A concentration of the analytes is thus achieved. 

Table 3.44 Characteristics of solid-phase extraction Advantages...

More recently, several aroma compounds were isolated from cupuacu pulp by vacuum distillation, solid-phase extraction, and simultaneous steam distil-lation-extarction and were analysed by GC, GC-MS, and GG-O [8]. The olfaction of the extracts obtained by solid-phase extraction indicated linalool, a-ter-pineol, 2-phenylethanol, myrcene, and limonene as contributors of the pleasant floral flavour. In this study, the esters ethyl 2-methylbutanoate, ethyl hexanoate, and butyl butanoate were involved in the typical fruity characteristics. 

Niederer [100] used ion trap mass spectrometry and negative ion chemical ionisation to determine nitro- and oxypolyaromatic hydrocarbons in soils. Meyer et al. [101] have described a simple and reproducible method which provides the simultaneous determination of polycyclic aromatic hydrocarbons and het-eropolycyclic aromatic hydrocarbons (N, S, O) and their metabolites in contaminated soils. Contaminants extracted from the soil sample were separated by polarity and acid-base characteristics using solid-phase extraction on silica gel and a strong basic anion exchange material. A subfraction containing PANHs and neutral metabolites was subsequently fractionated into neutral and basic... 

Table 3.10 Chromatographic Modes and Elution Characteristics for Solid-Phase Extraction Devices3...

The choice of the sorbent is dictated by the characteristics of both the analytes and their potential interferences. The sorbents most frequently employed here are silica, alkylsilane-modified silica (bonded phases), alumina, porous polymers (with and without ion-exchange groups) and carbon-based materials. One typical application is a method for the determination of hexavalent chromium in soils [10] using the on-line system depicted in Fig. 4.9. After USAL, the analytes in the leachate were directly determined or preconcentrated depending on their concentration. Concentration was performed by on-line solid-phase extraction using a laboratory-made minicolumn packed with a strong anion-exchange resin. The absolute limits of detection were 4.52 and 1.23 ng without and with preconcentration, respectively. 

Solid-phase extraction (SPE) is one of the most commonly used sorbent extraction techniques. The analytes are extracted together with interfering compounds with some similar characteristics by passing a usually aqueous sample through a plastic cartridge containing dispersed sorbent on a particulate support. A selective organic solvent is normally used to remove interferences and a different solvent is then employed to elute the retained analytes. This technique has a number of attractive features as compared with traditional solvent extraction. Thus, it is quite simple and inexpensive, can be automated and used in the field, and uses relatively small amounts of solvents. Particle-load... 

The impact of the extraction conditions using various solvents on the recoveries has never been studied in detail, and the results have never been compared. The introduction of modern extraction methods, such as microwave-assisted extraction, supercritical fluid extraction, and solid-phase extraction, probably will improve the efficiency of extraction, even in the instance of unstable pigments and pigment mixtures. The majority of TLC separations were carried out on traditional silica layers. As the chemical structures and, consequently, the retention characteristics of pigments are highly different, a wide variety of eluent systems has been employed for their separation, consisting of light petroleum, ethyl formate, ethyl acetate, benzene, toluene, chloroform, methanol, n-butanol, formic or acetic acid, and so forth. 

Preparative HPLC is typically the technique of choice for impurity purification. It is often necessary to enrich the impurity before preparative HPLC purification. Various techniques such as solid-phase extraction can be used to enrich the low-level impurity. To ultimately confirm the structure of a new impurity, it may be necessary to synthesize the compound and compare its spectroscopic characteristics to those observed in the original sample. A very effective means of getting useful structural information is to conduct a degradation study on the purified impurity. 

Levels of radioactivity were highest in the liver and kidneys of male and female rats at two hours post final dose and averaged 3.A63 ug equivalents/g and 4.073 ug equivalents/g in male and female rat liver, respectively, and 2.383 and 2.132 yg equivalents/g in male and female rat kidney. Urine samples were analyzed by direct injection onto the HPLC column, whereas feces and liver samples were homogenized and extracted with methanol and subjected to solid phase extraction (if necessary) prior to HPLC analysis of the organic extract. The major radiolabeled component in male and female rat urine co-chromatographed with flunixin. Lesser amounts of the two hydroxylated metabolites, 5-hydroxyflunixin and 2 -methyIhydroxyflunixin, were also detected. Two major radiolabeled residues, identified by retention characteristics as flunixin and 5-hydroxyflunixin, were observed in rat feces. The major radiolabeled component in male and female rat liver co-chromatographed with authentic flunixin standard. The monohydroxymetabolite, 5-hydroxyflunixin was also detected in male rat liver. 

Dereplication and characterization The characteristic binding profile of a compound on a number of solid phase extraction resins can be used for comparative and dereplication purposes. Compounds that bind differently to the same media must be different, and if a series of extracts is suspected of containing the same unknown natural product (e.g., all the extracts possess the same biological activity), the fact that they all exhibit the same binding profile might lead to a decision to first isolate the component from one of the extracts, then use that as a standard with which to examine the other extracts. 

Since the last decade, the hypercrosslinked polystyrene sorbents have also come into routine use in analytical chemistry. They are widely used as excellent solid-phase extraction (SPE) media for the pre-concentration of trace amounts of organic contaminants in the environment, food products, biological fluids, gases, aquatic pools, etc., in combination with various chromatographic analytical techniques. By now many companies offer fine beads or granular particles of hypercrosslinked sorbents for SPE. Their main characteristics are presented in Table 9.7. 

Solid phase extraction A process used to separate compounds from a mixture based on their chemical and physical characteristics Solubility A measure of the amount of solid required to be added to a given volume of solvent in order to form a saturated solution Solvent A substance that can dissolve another substance to form a solution. 

For solid phase extraction, an ideal MIP adsorbent should have the following characteristics High binding affinity, specificity and capacity fast association and disassociation kinetics broad solvent compatibility and long-term stability. 

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